Measurement of W boson helicity fractions in t anti-t decays at DZero and CDF Page: 3 of 4
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o 25 D , L = 1 fb-' (a)
2 20 - '
l.u 15--
10 - _ -
5 -
-1 -0.5 0 0.5 1
cosO*CDF Run II PreliminarV
-1 -0.5 0 0.5 1
COS(0)0
w40 DO, L = 1 fb1 (e)
30 -- -
20-
10-
4-1 -0.5 0 0.5 1
CoO*SCDF Run II Preliminary Entnes 430
70 backgroundd
70 --- - .+left-handled
--+longiltldnal
60 _ t data 1 8 fb-
30 -
20
10
1 -. -0. -0.4 -0. 0 0.2 -- . 0.6.1.0. --Figure 2: Reconstructed cos O* in the DZero f+jets channel (top left) and in the DZero
dilepton channel (top right). Reconstructed cos O* in the CDF f+jets channel with the
unfolding method (bottom left) and CDF template method (bottom right).
dijets. The f+ parameter is set to zero and matrix elements are employed to generate a
likelihood L(fo, CS) for N events:
L(fo, Cs) H I1 C8P1(t2; fo) + (1 C8)Pw+jets(y2)
where C, is the fraction of signal events. Then fo is extracted from the likelihood. The
probabilities P(7) are derived for signal tt and background (W+jets) by evaluating the
leading order matrix elements at the measured vectors 7:
P(Y) =o-- f dajf (I1)f (42)W(Y, j)d1d2didjtdj
where f are the parton density functions, W(7, y) is a transfer function describing the
probability that parton with 5 will be measured as 7. As a crosscheck, the e and p channels
are evaluated separately. In the electron channel, fo = 0.660 0.111(stat) while in the muon
channel fo = 0.609 0.128(stat).
CDF Template Method. The CDF template method analysis uses the f+jets channel
and suffers background mainly from W+jets. Background is suppressed by requiring one e
or p, ET"18, scalar HT > 250 GeV, four or more jets, one of which is identified as a b-jet by
a secondary vertex tagger. The cos 0* distribution is fit with a 3rd degree polynomial times
two exponentials. An unbinned extended likelihood fitter is used to extract f+ and fo with
the likelihood:
= G(bpb, Ob) x P~s + blps + Pb) x HI 1 [bpb(c) + (1 fb)ps(c) -DIS 2008
150
100-50-
- Ln = 1.9 fb- (I 7,- F - )
N - >CD
Nb-tags >1
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Potter, Christopher Thomas. Measurement of W boson helicity fractions in t anti-t decays at DZero and CDF, article, April 1, 2008; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc929938/m1/3/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.